1. Field of the Invention
This invention relates to fluid purification systems and more particularly to fluid purification systems incorporating fluid exposure to both ultraviolet radiation and filtration.
2. Description of the Prior Art
In an attempt to provide high quality, potable drinking water, various treatment systems have been developed. Many such systems employ activated carbon filters, as a common treatment to remove odor, improve taste, and remove chemicals, such as chlorine and chloroforms. However, carbon is a nutrient source that supports bacteria life and growth. As a result, unless these filters are replaced frequently, the filters themselves provide a breeding ground for bacterial contamination. This bacteria is spread to the consumer as the water flows through the filter, picking up the bacterial contamination and delivering the bacteria to the user.
It has been found that activated charcoal filters are so conducive to bacterial growth that filters not routinely replaced may provide more bacterial contamination to the water than the unfiltered water itself. In addition, the bacteria tend to occupy many of the absorptive sites in the filter, reducing the filter's absorptive capacity and rendering the filter ineffective for its intended purpose of purifying the water.
It is well known that exposure of water to ultraviolet radiation kills microorganisms and bacteria carried by the water. For this reason, many conventional purification systems employ an ultraviolet sterilization unit in series with a filtration unit.
For example, U.S. Pat. No. 3,550,782 to Veloz discloses a water sterilizer apparatus having a pair of parallel water carrying tubes, and a string of ultraviolet bulbs located between the tubes. A reverse osmosis unit is connected in series between the tubes, so that the water flowing through the tubes is exposed to ultraviolet radiation both upstream and downstream of the reverse osmosis unit. The Veloz '782 patent states that the destruction of bacteria upstream of the reverse osmosis unit is desirable in order to protect the membrane of the unit against the accumulation of live bacteria. The filtered and sterilized water is stored in a large tank, from which water is drawn on demand.
The apparatus disclosed in the Veloz '782 patent may be suitable for some applications, but is impractical for home, domestic use.
First, the tank used in the Veloz system may act as a further breeding ground for microorganisms and bacteria, especially if the water remains in the tank for any extended period of time. The tank is connected to the faucet or water outlet, and bacteria may enter the tank through the faucet. Also, the tank may require periodic flushing or cleaning, to remove bacteria laden water as well as sediment and the like. Furthermore, unless the tank is pre-sterilized prior to its use, or sterilized periodically during use (which would be an almost impossible task for the consumer to undertake), any water fed to the tank from the sterilizer unit would quickly become contaminated with bacteria.
Second, the Veloz apparatus employs straight-line liquid flow tubes adjacent to the string of ultraviolet bulbs. Such a straight-line configuration is impractical for installation in a private residence.
Size constraints of a home installed purification system are of paramount importance. A purification system for use in a private residence should be a compact unit, easily installable by the consumer, within a kitchen sink cabinet or a bathroom vanity, for example.
The storage tank of the apparatus disclosed in the Veloz '782 patent requires an inordinate amount of space. Furthermore, if the storage tank were omitted from the Veloz system and the water was drawn on demand directly from the downstream tube, each tube would necessarily be of such length that it would be impractical to install the system in a private home.
For example, assuming that the average flow rate of water consumed in a private residence is one gallon per minute, and assuming that the string of bulbs provide an average of 90,000 microwatt seconds per square centimeter of ultraviolet radiation, then each tube of the Veloz sterilization unit would have to be at least 6 feet long, with a cross sectional area of 0.2 square inches, to effectively kill the bacteria and microorganisms carried by the water.
In addition, the apparatus disclosed in the Veloz '782 patent is not maximally effective in sterilizing the water and maintaining the reverse osmosis filtration unit in a bacteria free state. This is believed to be due to the straight-line path of the water through the flow tubes, which provide no turbulence to the water flow.